7. Characteristics of an Electrical Circuit
• Voltage (V)
– Voltage is the force, or “push,” that
causes electrons to move through a
circuit
– Provided by the pacemaker battery
• Current (I)
– Determined by the amount of
electrons that move through a circuit
– Cause myocardial cells to depolarize
• Impedance (R or W)
– The opposition to current flow
– All resistance: conductor, electrode,
myocardium
V
I R
10. Voltage and Current Flow
Electrical Analogies
Spigot (voltage) turned up, lots of
water flows (high current drain)
Water pressure in system is
analogous to voltage – providing
the force to move the current
Spigot (voltage) turned low, little flow
(low current drain)
11. Lead Impedance, 300~1500 Ohm
High impedance
Conductor failure, impedance >2500 Ohm
Low impedance
Insulation defect, Impedance <300 Ohm
12. The Revised NASPE/BPEG Generic (NBG)
Code for Antibradycardia Pacing
I
II
III
IV
V
Chamber(s)
Paced
Chamber(s)
Sensed
Response to
Sensing
Rate
Modulation
Multisite
Pacing
O = None
O = None
O = None
O = None
O = None
A = Atrium
A = Atrium
T = Triggered
R = Rate
A = Atrium
V = Ventricle
V = Ventricle
I = Inhibited
D = Dual (A + V)
D = Dual (A + V)
D = Dual (T + I)
modulation
V = Ventricle
D = Dual (A + V)
S = Single (A or V) S = Single (A or V)
NASPE is the North American Society of Pacing and Electrophysiology
BPEG is the British Pacing and Electrophysiology Group
BERNSTEIN, et al.; PACE 2002; 25:260–264
16. General Setting of Pacemaker
Parameter
Base Rate
Description
Pacing timing cycle
Maximum Sensor
Rate (MSR) is the
Max.
highest pacing rate
Sensor rate
allowed by ratemodulated pacing
Max
Tracking
Rate
upper limit of the
ventricular pacing
rate in response to
the patient’s intrinsic
atrial activity
Setting
Recommendation
•Depends on patient’s need Hysteresis
•Nominal setting 60-70 bpm Rest rate
•Depends on patient’s age
and activity (220-Age)X0.85
•Depends on patient’s age
and activity (220-Age)X0.85
•Also has to consider the
other cardiac disease
17. General Setting of Pacemaker
Parameter
Description
Setting
• AVB : 200-150
• SSS : depends on
the AV conductivity,
nominal less than
300ms
Recommendation
Reduce unnecessary
ventricular pacing
VIP/AICS/AV
hysteresis /MVP
AV/PV delay
AV : internal of Ap to Vp
PV : interval of As to Vp
Rate
responsive
AV/PV delay
shorten AV/PV Delay when
the atrial rate is higer then 90
bpm, to mimic physical
Off, slow, mid, high
demand, also allows setting
higher MTR
Pulse
Amplitude,
Pulse width
(A, V)
determines how much
electrical potential is
applied to the myocardium
during the pacing stimulus
Nominal setting
2.5V@0.4ms
• 2-3 times of
threshold to
secure capture
• AutoCapture
A/V
sensitivity
This parameter determines
the amplitude of signals to
which the device’s sense
amplifiers will respond
• A : 0.5~1.0 mV
• V : 2~3 mV
Higher level indicate
less sensitive to P/R
wave
18. Pacemaker Code
• Very useful in helping you understand how
the IPG is interpreting events
• Code:
– AS Atrial Sense
– AP Atrial Pace
– AR Atrial Refractory
– VS Ventricular Sense
– VP Ventricular Pace
– VR Ventricular Refractory
29. Lower Rate Interval (LRI) - VVI
• The lowest rate the pacemaker will pace the heart
in the absence of intrinsic events
LRI
LRI
30. Hysteresis
• Allows the rate to fall below the programmed
lower rate following an intrinsic beat
60 bpm
50 bpm
31. Rest Rate
• Allows the pacemaker to decrease the base rate to
•
•
the programmed auto rest rate during periods of
inactivity.
People spend about 7 hours, out of a 24 hour day,
sleeping, therefore 29% of the time is spent
sleeping.
The pacemaker calculates where this 29% would
occur based on the Activity Variance Histogram and
establishes this point as threshold.
32. “R” = Rate Response
• When the need for oxygenated blood increases, the
pacemaker ensures that the heart rate increases to
provide additional cardiac output.
34. Rate-Adaptive Pacing: Accelerometer
Accelerometer
•
•
•
•
•
•
Low current drain
Easy to manufacture
Rapid response to onset of activity
Compatible with standard pacing leads
Not responsive to pressure applied to can
Used in all current St. Jude Medical
pacemakers (began with Trilogy DR+)
Circuit Board
35. Rate-Adaptive Pacing
• The Sensors—Physiology
– Evoked response
• The QRS depolarization decreases
in area with exercise
• Works only when the device is
pacing
– QT interval
• QT interval shortens with exercise
• Works only when the device is
pacing
37. Upper Rate Response
• Dual-chambers pacemakers try to maintain 1:1 AV
synchrony but this is not always possible
• In the presence of high intrinsic atrial rates,
pacemakers may revert to upper rate responses
38. Upper Sensor Rate
• Defines the shortest interval (highest rate) the
pacemaker can pace as dictated by the sensor (AAIR,
VVIR modes)
40. Upper Tracking Rate (UTR)
• The maximum rate the ventricle can be paced in
response to sensed atrial events
Lower Rate Interval
{
Upper Tracking Rate Limit
SAV
AS
VP
VA
SAV
AS
VA
VP
DDDR 60 / 100 (upper tracking rate)
Sinus rate: 100 bpm
41. Upper Rate Behavior
Ventricular Rate
UTR
LR
1:1 Atrial
Tracking
No
Ventricular
Pacing
LR
= Ventricular Pacing
Wenckebach
UTR
Atrial Rate
TARP
2:1 Block
45. Wenckebach vs. 2:1 Block
• If the upper tracking rate interval is longer
than the TARP, the pacemaker will exhibit
Wenckebach behavior first.
• If the TARP (total atrial refractory period) is
longer than the upper tracking rate interval,
then 2:1 block will occur.
50. Benefits of Dual Chamber Pacing
• Provides AV synchrony
– Lower incidence of atrial fibrillation
– Lower risk of systemic embolism and stroke
– Lower incidence of new congestive heart failure
– Lower mortality and higher survival rates
56. Blanking and Refractory Periods
• Blanking Period
– A period of time during which the sense amplifiers
are off, and the pacemaker is “blind”.
– Designed to prevent oversensing pacing stimulus
• Refractory Period
– A period of time during which sensed events are
ignored for timing purposes, but included in
diagnostic counters
– Designed to prevent inhibition by cardiac or noncardiac events
57. Why Do We Use Refractory and
Blanking Periods?
• Pacemaker sensing occurs when a signal is large
enough to cross the sensing threshold
5.0 mV
Sensing does not tells us
anything about the origin or
morphology of the sensed
event, only its “size.”
2.5 mV
1.25 mV
1.25 mV Sensitivity
Time
58. Why Do We Use Refractory and
Blanking Periods?
• By manipulating the sense amplifiers, we filter
signals based on their relationship
The potential for digitizing
these signals may someday
allow pacemakers to
discriminate signals based
on morphology rather than
just on their relationship.
5.0 mV
2.5 mV
SENSE!
1.25 mV
Sensing
Blanking
Time
Refractory
59. Blanking Periods
• Atrial Blanking (AB)
– A non-programmable atrial blanking period (50-100 ms) from
atrial paces or senses.
– Avoid the atrial lead sensing its own pacing pulse or P wave
(intrinsic or captured).
• Ventricular blanking (VB)
– 50-100 ms in duration and is dynamic, based on signal strength.
– After a ventricular paced or sensed event to avoid sensing the
ventricular pacing pulse or the R wave (intrinsic or captured).
• Post ventricular atrial blanking (PVAB)
– Initiated by a ventricular pace or sensed event (220 ms)
– Avoid the atrial lead sensing the far-field ventricular output
pulse or R wave.
60. Ventricular Blanking
• The first portion of the refractory period
• Pacemaker is “blind” to any activity
• Designed to prevent oversensing pacing stimulus
Lower Rate Interval
VP
Blanking Period
Refractory Period
VP
VVI / 60
61. Blanking Periods
Ventricular Refractory and Blanking Periods
PVAB
ARP
Post Atrial
Ventricular
Blanking
PVARP
VRP
Ventricular Refractory
Period
Ventricular
Blanking
62. AV Crosstalk
• Atrial pacing spike will be detected in the ventricle.
• Will inhibit ventricular pacing
64. Blanking Periods
Atrial Refractory and Blanking Periods
Post Ventricular Atrial
Blanking
Atrial Blanking
PVAB
ARP
PVARP
VRP
Atrial Refractory Period
Post Ventricular Atrial
Refractory Period
65. Refractory Periods
• VRP and PVARP are initiated by sensed or paced
ventricular events.
– The VRP is intended to prevent self-inhibition such as
sensing of T-waves.
– The PVARP is intended primarily to prevent sensing of
retrograde P waves, far-field R wave, or premature atrial
contractions.
66. Ventricular Refractory Period
1000 ms
1000 ms
VRP 320 ms
Blanking
V
P
VRP 320 ms
V
R
V
P
Refractory
• Pacemaker VRP avoids the sensing of :
–
–
–
–
–
Its own stimulus
The paced QRS complex
The T wave
(Excessive) afterpotential
The combination of T wave and afterpotential
V
R
69. Prevention of PMT
• Prevention
– Extend PVARP (Post Ventricular Atrial Refractory
Period)
– Program PVARP 50 ms longer than measured
retrograde VA conduction (RVAC)
• Use VVIR mode to determine the RVAC
73. AV Delay or AV Interval (AVI)
• AVI is the interval between an atrial event (either sensed or
paced) and the scheduled delivery of a ventricular stimulus.
• Typical sAVI is 30-50 ms shorter than pAVI (sAVI < pAVI).
• The AV intervals may be programmed to fixed values or
rate-adaptive (i.e. shortening with increasing atrial rates).
77. Automatic Mode Switching (AMS)
• AMS turns off atrial tracking in the presence of
intrinsic atrial activity above a programmable atrial
rate cutoff.
• Mode will switch from tracking mode (DDDR, DDD)
to DDIR (non-tracking mode) when atrial
arrhythmia is detected.
• AMS can cause a sudden rate decrease as atrial
tracking.
• Ventricular pacing is decoupled from atrial events,
but rate responsive pacing is matched to metabolic
needs.
78. Mode Switch
• The device detects an atrial arrhythmia by constantly
comparing intervals with the programmed mode
switch detection rate.
MS
DDD / 60 / 120 Mode Switch ON
79. 減少右心室電刺激 = 減少心衰竭住院
及心房顫動
Risk of AF Relative to
DDDR Patient With
Cum%VP=0
MOST study
Every incremental 1% of unnecessary VP increases the
risk for Heart Failure Hospitalizations by 5.4%
There is a 1% increase in the risk of AF for each 1%
increase in cumulative right ventricular pacing.
Within 95%
Confidence
Risk of AF
Cumulative % Ventricular Pacing
80. Ventricular Intrinsic Preference (VIP)
• VIP activation
– Device extends AV delays by 160 ms searching for Rwaves for up to 3 cycles in our example
– R-waves found within 1 cycle, therefore, AV delay
remains at lengthened value
81. Ventricular Intrinsic Preference (VIP)
• VIP deactivation
– Device extends AV delays by 160 ms searching for Rwaves for up to 3 cycles in our example
– No R-waves found within 3 cycle, therefore, AV delays
returns to programmed values.
1
2
3
82. Ventricular Intrinsic Preference (VIP)
• VIP most beneficial
–
–
Intermittent AV block
Mild prolongation of AV conduction
• VIP not beneficial
–
–
–
Complete permanent AV block
Marked 1st degree AV block
If CRT therapy is indicated
• VIP clinical benefits
– Less risk of heart failure progression
– Less risk of developing AF
– Better QoL trough improved hemodynamics
83. MVP AAI (R) to DDD(R)Pacing (MVP)
Managed Ventricular
Operation
Switch from AAI(R) to Temporary DDD(R) Mode
Ventricular support if loss of A-V conduction is persistent.
2 out of 4 Most Recent A-A Intervals with No Conducted VS Event
No VS
Conduction
Ventricular Back-Up
Pace at 80 ms Post
the Scheduled AP
Switch to DDD(R) occurs after
back-up VP; programmed PAV/SAV are
used during this mode of operation
85. Cardiac Resynchronization Therapy
Goal: Mitigate dyssynchrony
through atrial synchronous
biventricular pacing
Right Atrial
Lead
Left Ventricular
Lead
Right Ventricular
Lead
• LV lead site: lateral = posterior > apical
• OptiVol thoracic impedance (MID-HeFT study): 和PCWP成反比
